Dicarboxylic acids, such as adipic acid, malic acid, fumaric acid and succinic acid are potential precursors for numerous chemicals. For example, succinic acid can be converted into 1,4-butanediol (BDO), tetrahydrofuran (THF), and gamma-butyrolactone (GBL) by hydrogenation reactions. Conventional methods may use gas phase hydrogen and deionized (DI) water as the medium for preparing reduced or pre-activated metallic catalysts. For example, U.S. Pat. No. 6,008,384, herein incorporated by reference in its entirety, discloses a process for preparing metallic catalysts using deionized water during the reduction procedure.
However, a variety of by-products, such as cyclic or linear ethers, acetals and low molecular alcohols, may be formed during the hydrogenation of some dicarboxylic acids to the corresponding diols. In the case of maleic, succinic and fumaric acids, such conventional methods results in the formation of significant amounts of THF or other by-products rather than the desired BDO. This necessitates additional separation steps to isolate the desired product from by-products, loss of yield and increased production cost.
Accordingly, there is a need for a means to achieve further improved selectivity in hydrogenation of hydrogenatable precursors to the desired product that avoids the formation of unwanted by-products.